Synthesis and Evaluation of pH Responsive Silica-Polymer Hybrid Nano Capsules

Abstract

The construction of pH responsive silica-polymer hybrid nano capsules is demonstrated here. Eleven to 12 nm sized gold nano particles (GNPs) were used as template to build the nanoshell. GNPs were coated with a layer of silica and over that a polymer coating was done using free radical polymerization of methacrylic acid. The gold core of the nano particle was leached out using the cyanide chemistry to form hybrid nano shells. The different stages of the formation of the silica layer, polymer layer, and the etching away of the gold core were followed by UV-Visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). A model compound Rhodamine B isothiocyanate was loaded into the shells to demonstrate the ability of the shells to modulate the release in response to external pH. At pH 1.98, the shells nearly stopped the release of the drug while at pH 7.0, 90% of the cargo was released. We monitored the stability of the guest loaded shells at pH 1.98 and found that even after several weeks the shells were intact. Our results show that the smart hybrid nano shells possess the ability to protect the entrapped molecules from the hostile pH of stomach and are suitable vehicles for the delivery of delicate drugs such as peptides through oral routes.